In electrical machine construction, any type and method of winding electrical conductors to form a coil is covered by the collective term coil winding technology. In this case, “coils” are not intended to be understood only as separate inductive passive components; rather, in the present context, the term covers all windings and winding materials that are suitable for generating or for detecting a magnetic field. The windings of actuators, in particular of the stator and rotor of a rotating electrical machine, are likewise called coils in the text which follows within this further meaning of the word.
The winding technology therefore substantially determines the properties of electromechanical assemblies which have windings. Said properties include the insulation resistance, the quality factor, the size required for a specific performance or magnetic force or else the magnetic stray field. Since the requirements in respect of energy efficiency according to the prior art increase greatly, there are, in particular, increasing demands for the development of components for electromechanical assemblies such as electric motors.
Winding operations in stators and/or in rotors are usually performed primarily with comparatively thin individual wires—typically with diameters of up to 2 mm—which are inserted into the openings in the stator or motor iron (slots) manually or by corresponding winding and pull-in machines. It is known to introduce bars, instead of individual wires, into the slots, to form said individual bars and then to connect, for example to weld, said bars at the ends to form a continuous winding. Since, according to the prior art, primarily short U- or V-shaped individual segments which are reminiscent of hairpins are used for this purpose, bar windings of this kind are sometimes called hairpin conductors in technical circles.
Bar windings provide various advantages over individual wire windings: whereas individual wire windings still require various manual steps during manufacture in spite of a high degree of automation, bar windings can be produced in a fully automatic manner. In this case, the bars usually have a rectangular cross section and are segmented into equal cross sections in the slot. Bar windings therefore allow better utilization of the slots than individual wires which, even with dense packing, leave empty spaces and cause a substantial loss of space due to insulation coating. Higher machine powers in small installation spaces can be achieved owing to the higher level of filling of the slots with copper (the so-called copper filling factor). Whereas filling factors of from 30% to 50% are common in the case of individual wires, even more than 80% can be achieved with bar windings. More reliable insulation both between the bars and also between bars and irons is possible owing to the well-defined surface and the relatively large dimensions of the hairpin or bar conductors. The degradation of the insulation is one of the most important aging mechanisms and central to the service life of electrical machines. In the case of U-shaped segments, the individual segments can be inserted into the slots on the end side during manufacture, as a result of which slots which are closed toward the air gap and are half open can be realized, this being difficult or even impossible in the case of individual wire windings with continuous wire, as explained in U.S. Pat. No. 8,330,318, which is incorporated by reference herein. If the electrical machine with a bar winding is operated in high rotation speed ranges, the losses of the electrical machine increase on account of high-frequency effects.
JP 2011 147 312 A, which is incorporated by reference herein, describes a stator winding of an electrical machine, wherein different winding cross sections are provided within the slots. In this case, the windings with a relatively small cross section are preferably situated further on the inside than the windings with a relatively large cross section.
US 2004 0207 284 A1, which is incorporated by reference herein, describes an electrical machine with a stator winding comprising radially arranged conductor segments with a rectangular cross section.
US 2012 0025 660 A1, which is incorporated by reference herein, describes an electrical machine with a stator winding having a large number of turns with a rectangular cross section. In this case, each turn consists of two sections, wherein the inner section of a turn is connected to an outer section of a turn in a non-adjacent slot.
US 2012 0274 172 A1, which is incorporated by reference herein, describes an electrical machine with a stator winding comprising a large number of line bundles, wherein the cross section of the line bundles is flexible. In this case, the line bundles are arranged such that adjacent line bundles are in contact.
US 2015 0311 757 A1, which is incorporated by reference herein, describes an electrical machine with a stator winding comprising a large number of coil conductors. In this case, the coil conductors can have different, in particular also curved, cross sections.
US 2016 0013 692 A1, which is incorporated by reference herein, describes a stator for an electrical machine with a large number of turns which are radially arranged and of which the cross section changes depending on their position.
U.S. Pat. No. 5,801,471 A, which is incorporated by reference herein, and U.S. Pat. No. 6,252,327 B1, which is incorporated by reference herein, disclose further prior art in respect of stator windings for electrical machines.